1. Field of the Invention
The present invention relates generally to a removable conditional reception module for supporting a Conditional Access System (CAS) for a pay broadcast channel in an OpenCable scheme. More particularly, the present invention relates to broadcast reception system, apparatus, and method for carrying out a CAS function without a cablecard, which includes a removable conditional reception module.
2. Description of the Related Art
Past analog pay broadcasting systems employ a conditional reception technique that merely generates distortion in a transmitted signal and allows a receiver to remove the generated distortion in order recover the signal. As broadcasts become digitized, new conditional reception techniques for encrypting the transmit data based on subscriber authentication and decrypting the data at a receiver have been introduced. The Conditional Access System (CAS) gives or restricts the right to view broadcast programs in a paid broadcast. In the CAS, the conditional reception function is carried out by a cablecard.
FIG. 1 illustrates a simplified diagram of the conventional CAS based on the cablecard.
Referring to FIG. 1, a headend 100, which is a broadcasting system for transmitting the broadcast, transmits audio, video, and data over a single channel using a Multiplexer (MUX) 102. The transmitted broadcast signal is scrambled by a Control Word (CW) and an Entitlement Control Message (ECM) to restrict the authorization to view the broadcast program. The headend 100 separately transmits Out Of Band (OOB) data. The OOB data 106 includes an Entitlement Management Message (EMM), Service Information (SI), etc. The SI is fed to a navigator 122 of a set-top box 110 and the EMM is fed to a security processor 140.
The set-top box 110, which receives the digital broadcast signal includes a tuner 112, a modulator 114, a DEMUltipleXer (DEMUX) 116, a decoder 118, a cable modem 120, the navigator 122, and a second descrambler 124. The tuner 112 receives the broadcast signal from the headend 100, tunes to an intended broadcast signal, and outputs the tuned broadcast signal to the modulator 114. The modulator 114 demodulates the tuned broadcast signal to a digital bit stream. The bit stream includes video, audio, and data stream, and also includes the ECM information. The video, audio, and data streams are output to a cablecard 130. The ECM 150 is fed to a security processor 140. The second descrambler 124 receives an encrypted Copy Protection (CP) key and the scrambled broadcast signal from the cablecard 130, decrypts the CP key, and descrambles the scrambled broadcast signal (including audio, video, and data signals) using the decrypted CP key. The DEMUX 116 splits the audio, video, and data signals from the descrambled broadcast signal and provides the separated signals to the decoder 118. The decoder 118 decodes the video, audio and data streams into a format that can be processed by a TV set. The cable modem 120 converts an analog signal to a digital signal to enable the use of high-speed Internet over a cable network. The cable modem 120 is used for two-way broadcasting according to the Data Over Cable Service Interface Specification (DOCSIS) Set-top Gateway (DSG) scheme. The navigator 122 provides program information to a user based on the SI fed from the headend 100.
The cablecard 130 is installed into the set-to box 110 according to a defined interface standard. A first descrambler 132 of the cablecard 130 descrambles and restores the scrambled broadcast signal output from the set-top box 110 using the CW provided from the security processor 140 and outputs the restored broadcast signal 160 to the scrambler 134. The scrambler 134 re-scrambles the descrambled broadcast signal under the control of the security processor 140 and outputs the scrambled broadcast signal to the second descrambler 124 of the set-top box 110. That is, the scrambler 134 scrambles the broadcast signal using the CP key according to a Copy Protection Protocol 190 and outputs the scrambled broadcast signal to the second descrambler 124 of the set-top box 110 together with the CP key.
The security processor 140 restores the ECM from the EMM and extracts the CW from the restored ECM. The extracted CW is provided to the first descrambler 132.
When the cablecard 130 is installed into the set-top box 110 and executes the CAS function, the pay broadcast service is provided. Users can enjoy the services from the multiple providers by installing various cablecards 130, which are provided by various broadcast service providers, respectively, into the set-top box 110.
As stated above, the CAS of the cablecard 130 descrambles the scrambled contents transmitted from the headend 100 with the CW provided from the security processor 140, scrambles the descrambled broadcast signal according to the copy protection protocol, and transmits the scrambled broadcast signal to the set-top box 110. The set-top box 110 restores the contents by descrambling the broadcast signal using the CP key and allows viewing of the paid broadcast by decoding the restored contents at the decoder 118. To generate the CP key, the cablecard 130 and the set-top box 110 verify whether the cablecard 130 and/or the set-top box 110 are authorized through the mutual authentication using X.509 certificates issued by OpenCable Trust Authority (TA). More specifically, the cablecard 130 and the set-top box 110 perform the mutual authentication using a Public Key Infrastructure (PKI) structure, and the set-top box 110 can output the paid broadcast provided from a plurality of headends without belonging to a particular CAS.
However a disadvantage of the conventional cablecard system is that, the cost of cablecards can be burdensome for consumers. Further, the heat generated from the cablecard may bend or deform the cablecard, or increase the temperature within the set-top box. Even further, the physical interface of the conventional cablecard increases the complexity of hardware and circuitry in the set-top box. Even further, in the conventional cablecard system, a channel change speed is lowered, due to the constraints of the signaling speed with the cablecard and the dual protection structure (scramble+CP) of Moving Picture Experts Group (MPEG)-2 Transport Stream (TS) transmission.